Heath Pois

Hybrid enabled thin film metrology using XPS and optical

Complexity of process steps integration and material systems for next-generation technology nodes is reaching unprecedented levels, the appetite for higher sampling rates is on the rise, while the process window continues to shrink. Current thickness metrology specifications reach as low as 0.1A for total error budget – breathing new life into an old paradigm with lower visibility for past few metrology nodes: accuracy. Furthermore, for advance nodes there is growing demand to measure film thickness and composition on devices/product instead of surrogate planar simpler pads. Here we extend our earlier work in Hybrid Metrology to the combination of X-Ray based reference technologies (high performance) with optical high volume manufacturing (HVM) workhorse metrology (high throughput). Our stated goal is: put more “eyes” on the wafer (higher sampling) and enable move to films on pattern structure (control what matters). Examples of 1X front-end applications are used to setup and validate the benefits.

Performance of measuring contact holes using the Opti-Probe 7341 3-D RT/CD technology

Spectra of contact hole arrays with target diameters ranging from 106 to 131 nm and pattern pitch ranging from 220 to 300 nm are taken from an off-axis (65°) rotating compensator spectroscopic ellipsometry (RCSE).[1] 3-dimensional finite difference (FD3D) model developed by H. Chu,[2] is applied in the studies. To ensure accuracy of optical dispersion of each film, the simultaneous use of angle resolved beam profile reflectometry (BPR), broadband spectroscopic reflectometry (BB), and SE of an Opti-Probe 7341 are used for characterizing of the resist and BARC films. In particular, The extracted n&k dispersions are used to model the contact hole SE data using Therma-Waves proprietary 3-dimensional RT/CD technology.[3,4] The performance of stability of both static and dynamic repeatability, uniformity, and correlation to other independent technology (i.e., SEM) will be presented in this paper.

Optical characterization of 193nm amorphous carbon ARC films

In this study, the optical properties of amorphous carbon (aC) ARC films are investigated using an Opti-probe OP7341, and a metrology solution that robustly measures a broad range of process conditions is presented. We find that the aC material is consistent with uni-axial anisotropy, and that this effect may have important implications for photolithography. These results are obtained through the combination of multiple technologies in one tool: spectroscopic ellipsometry (SE); spectroscopic reflectometry or broadband (BB), with a wavelength range of 190-840 nm; single wavelength (673 nm) but multiple incident angle beam profile reflectometry (BPR) and beam profile ellipsometry (BPE), and single wavelength (633nm) absolute ellipsometry (AE). The combination of technologies at multiple angles and wavelengths provides additional optical information and sensitivity not possible with single-technology approaches. A complex wavelength dependent anisotropy model was developed for this analysis, and is compared with a real anisotropy model. The complex anisotropy model and the effective medium approximation (EMA) with two and three components were applied to a set of 12 wafer set with thickness swing aC films in the range of 500-750 Å as well as a second set of 23 pre- and post- etch wafers. The complex anisotropy model clearly has the advantage of best fit the BPR profiles along with the SE Fourier coefficients. The etch rate obtained by the complex anisotropy also showed a much narrower variation as compared with the EMA2 and EMA32 models with the real anisotropy.

Strained-silicon metrology using a multi-technology optical system

A selection of thin Si layers grown epitaxially upon thick relaxed SiGe films were measured using the combination of optical metrology techniques available on the Opti-Probe 7341 system. The techniques used included in particular (i) angle resolved laser Beam Profile Reflectometry (BPR) with S and P polarization, (ii) Broad-band visible-DUV spectrophotometry (BB), and (iii) spectroscopic ellipsometry (SE). The measured parameters included the Ge-content of the relaxed SiGe layer, the thickness and optical dispersion of the thin Si layer, and the thickness of the native oxide layer on the strained Si. Strain in the Si layer can be recognized by a significant downwards shift in the energy of the E1 peak and in the magnitude of the E2 peak in the ε2 dispersion curve, which is consistent with theoretical predictions when the strain in the layer is tensile. The thickness measurements of the Si layer made by the Opti-Probe were found to be in agreement with subsequent SIMS analysis to within 5Å for the strained-Si layer. Measurement precision for thickness was <1.5Å (3σ). for the strained-Si layer. Overall, the results show that a reliable and stable measurement of Strained-Si is possible using optical metrology.

Graded Si1−xGex Metrology Using a Multi‐Technology Optical System

Graded Si1−xGex structures have been measured with good accuracy, stability and tool‐tool matching by utilizing different measurement methods in one system (Opti‐Probe®). The measurement methods utilized are (i) laser reflectivity versus angle for S and P polarization (BPR®), (ii) visible‐DUV reflectometry (BB), and (iii) spectroscopic ellipsometry (SE). An alloy dispersion model, along with a multi‐layer linear graded‐material model, were used to process the data and extract the thickness of the cap‐Si, graded and spacer Si1−xGex layers, as well as the Ge%, simultaneously. The results were found to be in agreement with subsequent SIMS analysis to within 50A for all layers and 0.5% atomic Ge%. Stability and matching results for thickness were <13A (3σ) for all layers, and for the Ge% the stability was <0.25–0.6% (3σ).

XPS-XRF hybrid metrology enabling FDSOI process

Planar fully-depleted silicon-on-insulator (FDSOI) technology potentially offers comparable transistor performance as FinFETs. pFET FDOSI devices are based on a silicon germanium (cSiGe) layer on top of a buried oxide (BOX). Ndoped interfacial layer (IL), high-k (HfO2) layer and the metal gate stacks are then successively built on top of the SiGe layer. In-line metrology is critical in precisely monitoring the thickness and composition of the gate stack and associated underlying layers in order to achieve desired process control. However, any single in-line metrology technique is insufficient to obtain the thickness of IL, high-k, cSiGe layers in addition to Ge% and N-dose in one single measurement. A hybrid approach is therefore needed that combines the capabilities of more than one measurement technique to extract multiple parameters in a given film stack. This paper will discuss the approaches, challenges, and results associated with the first-in-industry implementation of XPS-XRF hybrid metrology for simultaneous detection of high-k thickness, IL thickness, N-dose, cSiGe thickness and %Ge, all in one signal measurement on a FDSOI substrate in a manufacturing fab. Strong correlation to electrical data for one or more of these measured parameters will also be presented, establishing the reliability of this technique.

CD variation control based on accurate characterization of 193-nm material and CD metrology

Shrinkage of device dimensions requires tighter lithography process control. Current levels of Process Control leave less than 0.5 nm budget for CD metrology. An accurate and stable metrology solution requires measurement of CD and profile that are critically dependent on thin film material characterization at various earlier process stages. Opti-Probe integrates five different technologies into a single platform to accurately characterize optical properties of 193 nm materials. Real-time CD (RT/CD) technology utilizes four independent spectra collected from the samples using a rotating-compensator spectroscopic ellipsometer (RCSE) and analyzes the spectra with an innovative numerical solution-finding approach to construct detailed CD and profile of printed features in a 2- and 3 Dimensional geometries. The study presents a comparison of: i) Methodologies using an advanced combination of metrology techniques to characterize 193 nm materials (e.g. ARC). ii) Measured CD and profile variations using RCSE of Opti-Probe and RT/CD technology. iii) Correlation between measured CD variation and measured material characteristics. In order to achieve less than 0.3 nm accuracy and stability requirement for sub 65 nm process development and CD uniformity control, less than 0.003 variation and accuracy in optical dispersion (n&k) of critical material has to be ensured.